Electron focusing system



Ot- 22, 1.940-y w. scHRoEDER ELEcTRoN Focusmc SYSTEM ld May 5,

IIIIIIIIJ 9 A y INVENTOR WILLY SCHROE'DER ATTORNEY pf/Ase aff/,Free

yPatented Oct. 22, 1.9.40

` U'NiTED STAT-Es' ELEc'rRoN FocUsING SYSTEM' :s

Willy Schroeder, Berlin, Germany, assigner to4 Telefunken Gesellschaftfr Drahtlose I1`elegraphie m. b. 'H.,!Berlin, Germany, a corporation ofGermany 'Application May-5.1939, seria1,No.`z71s,ss1

In'Germany April 22, 1938 'a clyaims'. (c1. 25o-2.7)

The-present invention relates to electron lens arrangement forelectron-ray tubes.' Ordinarily electron lenses are predicated upon theuse of electromagnetic or electrostatic fields, steady or v5L1invariahlewith time. In other Words, unless an Aarrangement comprising a`permanent magnet is concerned, they presuppose the provision of a D. -C.source of supply. The use of such a source of current supply seemedindispensable with a lll-'view to securing a position of the rayintersection point' (cross-over) or electron image ex,-y

hibitingtime invariability. As a matter of fact, electronvlen'sarrangements known in the prior art',` when yworkedwith A. C., would beunserv- However, v it isl frequently desirable to operate with A..C.purev l-,iceable for electron focusing.

i and simple, ormore particularly with alternating current furnishedfrom the conventional sup-r plyline` because i this makes for simplicityof 201 constructiony in general. v

-vThe invention discloses electron llens arrange.-v ments'ior electronraysv which are adapted tof be operated with A. C.vwithout the useofD-C.

V andv without the position ofthe focal;` point of'A '2'5 the electronray beingv altered in any undesirable f The invention vshall now vbe,discussed and exu ments of fundamentallyv equal`r action, say, two.

annularcoils of similar size and comprising equal 'y numbers of turns,andvif they are fed with two' sine currents yof like amplitude Inpresenting a phasedisplacement of 90v degrees,y that is, in

45..-quadratnre relation,` then their refractive power- .sind

However, since Smau-casar is `equa1 to 1, it

follows that the refractive power of the magi netic'lens underconsideration is proportional to y 5555102; 'in otherv words,independent of the time. Y

turns.

This holds'.tr'ueparticuiariy of the case that. l

the lenselds of the'two lens assemblies willf not-mutually influenceeach other to any lessential degree. ,l n f In:the case of coilscomprising different t1'.1rn- 5-` numbers, ampere-turns `in lieu ofcurrents imust;A be introduced in the above formula. The-fore# i goingconsiderations yhold good inV an analogous manner alsofor coils ofdissimilar forms, and` dissimilar diameters. But in such a casethecur-rf ll rents, of the coils must be `so chosen that the. focaldistances determined. by thev effective values: of the currents will beequal. l

i 'On the basis of these considerations, lens semblies areobtained'according to the-invention ,15C of the kind represented by-theeXempliedemf-t; bodiments of the appendeddrawing inA which Fig. 1l showsa catho'clelray tube whiche ern-"1. bodies-my invention .of two`magnetic coils fed With alternating currents nphase quadraturevlgo,

While l Y Fig. '2 vshows a Lmodiiicationfof theembodi-ff ment 'of myinvention in-Fig. 1` in Whichthreef coils are used; Fig. 3 shows twoalternating currents' in phase 52. quadrature yin graphical form forexplaining my; invention; Fig. 4 shows a further modification of theIembodiment shown in Fig. 1;

Fig. 5 shows schematically an arrangementlfor'r ggf l obtainingalternating currentsin phase quadi: vture fonusein .the embodimentsshown in Figsgi 1, Zand, 4, and f Fig. ,fshows .-'a modiiicationjof theembodiai" yment of my` invention, lin which electrostatic'ST5v focusingsystemsare used. i

In the simplest instance one may' usen-coils.; ofthe same d'ameter, andthe same numberof-izv Fig. l shows comprises the coils M1. andMz,coaxially ,positioned withre'spect to the cathode, ray tube,p2| havingan lelectron gun 25 for producing a beamlf of electronsand havingpositioneda target mem-iv ber 23 on the interior face thereof.l Thetarget.;

member 23 may convenientlvbe va uoresc'ent:

f screen, for example, in a television receiving tube,

or may;bea mosaic :electrode structure forfa-fz cathode 'ray televisiontransmitting tube. It will--1 i V be appreciated that deflectingsystems, lwhether v150'; i electrostatic or electromagnetic, mayalso-beproi-g.`

vvided for scanning the target member 23.1V iSince Y these are "wellknown'in the art', they are-notoL shown."

` .Through the coil M1: by wayAv of the terminals 155i'l an yelectroni'Alens system which; 0?

5 and 5a is caused to flow an alternating current of sine form, that is,of a kind as shown by the graph Si, Fig. 3. Through the coil M2 by wayof terminals and 6a is passed also a 5 sinusoidal A. C. having the samefrequency as the A. C. traversing coil Mi, While presenting a phasedisplacement angle thereto of.l 90 degrees, as shown` by curve S2 inFig. 3; By theaid of the system comprising coils i and 2 it is poslOsible to produce a sharp electron-optical image` or focus quite readilywith alternating current in a Way as above explained.

Fig. 2 illustrates another lens system Which is adapted to be energizedwith ArC. This organization comprises three constituent'coils, theVcentral one of these coils indicated at M4 containing the same numbero-f turns, asith'e two.- outer coils Ma and Ms combined. "IIhesaid.central coil M4 by Way of terminals 'i wand la,

is fed with an A. C. which has a phase displacement of. 90 degrees inrelation to the A; C. fed toitheouter. coils throughthe terminalsand 8a.Inside.4 the scopeA of the invention,.more than two, say, n coils couldbe used, each of the coils 25, being traversed. bythecurrentof a phaseof an n-phase supply line or network. The coils coordinated to thevarious phases could also be divided or splitVandf, similarlyas shownfor the coils M3 and Ma, Fig. 2, they couldbe disposed upon bothn sidesof one or. more coils which carry a current of different phase. So faras the relative spacing ofV the.coils.is concernedthis should be kept inmind, as. already pointed out, that the lens fields. of the constituentcoils vshould y not mutually react, for inthe same measure as suchmutual reaction occurs, the focus or pic-v ture sharpness will suffer,that is, be distorted, to a certain degree. In order that assatisfactory anrimage as possiblev may be secured, this 4,0,i generalrule will have tol be observed that the distance of the coils in axialdirection does-not` become lessi than: 1/3 the inside coil diameter. Thecoilsmay also be individually shielded to` avoid interaction.

The. arrangements ashereinV before described will'. generally be found.`serviceable for electronF optic imaging in which. the rotation of theelectron paths on' traversing.` the various coils does not disturb, thatis to say, for. instance, in the imaging of electron sources orapertures ofdiaphragms in picture scanning or picture rfc-creator#tubes, in oscillographic` tubes,. orV thev like. If the rotation dealtWith is such troublesome,.for instance, inthe imaging of a photo-cathodeof -largearea as used inwhat is known'. as picture converters ortransducers,.arrangements must be made sothat the rotation of the imageVoccurring at the frequency of the A..C`. Will be compensated. This isaccomplished by causing the cur.u rent of a certainphase to introducerotational actionsvvhich` will neutralize one another.

An exemplifiedembodiment of this nature is illustrated inFig. 4, M5,andMs andLMe and Mfs designate the coils which are traversed by A. C.

of a definite phase. All of the coils arevvound ini the same sense. Thecoils pertaining to one and the same phase, however, are traversed bycurrent in contrary direction, in a Way as'` indi(' cated byithe arrows.In this way, ifthe in- -tensities of the coil fields be properly chosen,

perfect compensation of' rotation is achieved.

In Fig. 5, I- have shown schematically the methodofobtaining thealternating currents in' phase quadrature. A source of alternatingcur-75..rent.. 3l. mayY be supplied'y directly to.v 'one of; the

coils, such as M1 through the terminals Si. A phase shiftingnetwork orphase shifter such as Well known in the art may be connected in parallelwith the source of alternating current 3| to shift the alternatingcurrent 90 degrees, the phase shifter being represented diagrammaticallyby the block 33, since-these are Well known in the art. The output ofthev phase shifter is then supplied through the terminals S2 to theVsecond of the tWo coils Mz in Fig. l. 10

Instead of lens assemblies which comprise electromagnetic lenses, itwould, of course, also be feasible'touse electrostatic lenses operatedin a corresponding manner with alternating potentials; theelectrostaticlenses being formed by the 15 eld set up between two or more lenselectrodes as shownv in Fig.6.

Inlig. 6-.is shown the electron gun 4| for producing a beam of electronsand the lens electrodes 153, 15, 47 and 49 enclosed Within an en- 20velope 5l. Suitable leads are provided fo-r supplying one alternatingcurrent potential Si to the. electrodes d3 and/l5, while an alternatingcurrent potential, in quadrature to Si is supplied from the source Satothe electrodes 41 and 49. 'I'here 25.= is thus provided alternatingelectrostatic. fields which are nphase quadrature.

Having describedmy invention, what I claim 1s:

1. The method of focusing'abeam; of electrons. 30 which comprisesproducing an alternating focus-1 ing magnetic field having axialsymmetry aboutthe beam of electrons, and producing a second alternatingfocusing magnetic eld longitudinally displaced from the first producedfield and in 35 phase quadrature with the first produced eld,. saidsecond produced field having axial symmetry with the electron beam.

2. lIfhe method of focusing a beam of ,electrons-i Which comprisesproducing.,l anvalter-nating focus- 40.,

ing magnetic field having axial symmetry about the beam of electrons,and producing a second alternating focusing magnetic field of amagnitude equal to the magnitude of the first produced fieldlongitudinally displaced from the first pro- 45,

duced field and in phase quadrature With the first` produced field, saidsecond produced field having axialsymmetry with the electron beam.

3. The method of focusing a beam of electrons which comprises producing.an alternating focus- 50A ing f eldhaving axial symmetry about the beamof electrons, and producing a second alternating' focusing fieldlongitudinally displaced from the rst produced field and in phasequadrature With l the first produced eld, said second produced 55- eldhavingv axial symmetry With the electron` beam.

4. The methodoffocusing arbeam of electrons' which comprises Y producingan` alternatingv focus ing field having axial symmetry about the beam 60of electrons, and` producing a second'alternating" focusing eldfof amagnituder equal to themag'- nitude of the first produced eldlongitudinally displaced from the irst produced field and in phasequadrature with the rst produced field, said second produced fieldhaving axial symmetry with the electron beam'.`

5. The method of focusing a beam of electrons. which comprises producingan alternating focus- 70 ing electrostatic eld havingY axial symmetryabout the beam of electrons, and producing a second alternating focusingelectrostatic eld longitudinally displaced from. the first-produced.

field. andin phase quadrature withthe rst pro-V f` for producing a beamof electrons, means for pro'-` ducing an alternating focusing magneticfield duced field, said second produced field having axial symmetry withthe electron beam.

6. The method of focusing a beam of electrons which comprises producingan alternating focusing electrostatic iield having axial symmetry aboutthe beam of electrons, and producing a second alternating focusingelectrostatic eld of a magnitude equal to the magnitude of the rstproduced field longitudinally displaced from the first produced eld andin phase quadrature with the rst produced fie1d,lsaid second producedeld having axial symmetry with the electron beam.

7. A cathode ray tube system comprising means for producing a beam ofelectrons, means for producing an alternating focusing magnetic fieldhaving axial symmetry about the beam o-f electrons, and means forproducing a second alternating focusing magnetic field longitudinallydisplaced from the first produced field and in phase vquadrature withthe rst produced field, said second produced field having axial symmetryWith the electron beam.

8. A cathode ray tube system comprising meansr having axial symmetryabout the beam o-f electrons, and means for producing a secondalternating focusing magnetic iield of a magnitude equal to themagnitude of the rst produced field longitudinally displaced from therst produced eld and in phase quadrature with the rst produced field,said second produced field having axial symmetry with the electron beam.

9. A cathode ray tube system comprising means for producing a beamy ofelectrons, means including an annular coil for producing an alternatingfocusing magnetic eld having axial symmetry about the beam of electronsand means including a second annular coil for producingy a secondalternating focusing magnetic iield longitudinally displaced from therst produced field and in phase quadrature with the rst produced eld,said second coil being longitudinally displaced from said first namedcoil by a distance greater than one third the annular diameter.

' WILLY SCHROEDER.

